All solid state battery

ABSTRACT

A main object of the present disclosure is to provide an all solid state battery in which occurrence of short circuit is inhibited. The present disclosure achieves the object by providing an all solid state battery comprising an anode including at least an anode current collector, a cathode, and a solid electrolyte layer arranged between the anode and the cathode; wherein a protective layer containing a Mg-containing particle that contains at least Mg, and also containing a polymer, is arranged between the anode current collector and the solid electrolyte layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2021-074697 filed on Apr. 27,2021, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an all solid state battery.

BACKGROUND ART

An all solid state battery is a battery including a solid electrolytelayer between a cathode and an anode, and one of the advantages thereofis that the simplification of a safety device may be more easilyachieved compared to a liquid-based battery including a liquidelectrolyte containing a flammable organic solvent.

For example, Patent Literature 1 discloses an all solid state batterycomprising, between an anode active material layer and a solidelectrolyte layer, a protective layer that includes a composite metaloxide represented by Li-M-O, provided that M is at least one kind ofmetal elements selected from the group consisting of Mg, Au, Al and Sn.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No.2020-184407

SUMMARY OF DISCLOSURE Technical Problem

From the viewpoint of improving safety of an all solid state battery,occurrence of short circuit is inhibited. The present disclosure hasbeen made in view of the above circumstances and a main object thereofis to provide an all solid state battery in which occurrence of shortcircuit is inhibited.

Solution to Problem

In order to achieve the object, the present disclosure provides an allsolid state battery comprising an anode including at least an anodecurrent collector, a cathode, and a solid electrolyte layer arrangedbetween the anode and the cathode; wherein a protective layer containinga Mg-containing particle that contains at least Mg, and also containinga polymer, is arranged between the anode current collector and the solidelectrolyte layer.

According to the present disclosure, a protective layer containing aMg-containing particle and a polymer is arranged between the anodecurrent collector and the solid electrolyte layer, and thus theoccurrence of short circuit may be inhibited in the all solid statebattery.

In the disclosure, an anode active material layer containing an anodeactive material that is at least one of a simple substance of Li and aLi alloy, may be arranged between the anode current collector and theprotective layer.

In the disclosure, the anode current collector and the protective layermay directly contact with each other.

In the disclosure, the Mg-containing particle may contain Li.

In the disclosure, the Mg-containing particle may not contain Li.

In the disclosure, an average particle size D₅₀ of the Mg-containingparticle may be 800 nm or more and 10 μm or less.

In the disclosure, a thickness of the protective layer may be 5 μm ormore and 100 μm or less.

In the disclosure, the all solid state battery may further comprise arestraining jig that applies restraining pressure along with a thicknessdirection of the cathode, the solid electrolyte layer and the anode, anda restraining pressure to be applied by the restraining jig may be 20MPa or less.

Effects of Disclosure

The present disclosure exhibits an effect of providing an all solidstate battery in which occurrence of short circuit is inhibited.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an example ofthe all solid state battery in the present disclosure.

FIG. 2 is a schematic cross-sectional view illustrating an additionalexample of the all solid state battery in the present disclosure.

DESCRIPTION OF EMBODIMENTS

The all solid state battery in the present disclosure will behereinafter explained in details.

FIG. 1 is a schematic cross-sectional view illustrating an example ofthe all solid state battery in the present disclosure. All solid statebattery 10 illustrated in FIG. 1 includes anode AN including anodeactive material later 1 and anode current collector 2, cathode CAincluding cathode active material layer 3 and cathode current collector4, and solid electrolyte layer 5 arranged between the anode AN and thecathode CA. Further, in FIG. 1, between the anode active material layer1 and the solid electrolyte layer 5, protective layer 6 that includes aMg-containing particle containing at least Mg, and also includes apolymer, is arranged. Incidentally, as shown in FIG. 1, the protectivelayer 6 may be regarded as a constituent element of the anode AN.

FIG. 2 is a schematic cross-sectional view illustrating an additionalexample of the all solid state battery in the present disclosure. Asshown in FIG. 2, all solid state battery 10 may not include an anodeactive material layer, and anode current collector 2 and protectivelayer 6 may directly contact with each other. Also, when the all solidstate battery shown in FIG. 2 is charged and lithium is depositedbetween the anode current collector 2 and the protective layer 6, theanode active material layer 1 (deposited lithium layer) shown in FIG. 1is obtained. In other words, the all solid state battery in the presentdisclosure may be a battery utilizing deposition-dissolution reactionsof a metal lithium.

According to the present disclosure, a protective layer containing aMg-containing particle and a polymer is arranged between the anodecurrent collector and the solid electrolyte layer, and thus theoccurrence of short circuit may be inhibited in the all solid statebattery.

In Patent Literature 1, in an all solid state battery utilizingdeposition-dissolution reactions of a metal lithium as an anodereaction, a protective layer containing a composite metal oxide Li-M-Ois arranged between the anode active material layer and the solidelectrolyte layer, so as to protect from deterioration of the solidelectrolyte due to the metal lithium and to suppress an interfaceresistance between the anode active material layer and the solidelectrolyte layer. Also, in Patent Literature 1, vapor-deposition of themetal element M onto the anode current collector is carried out tocharge, and bring into a reaction with Li, so as to form a protectivelayer containing the composite metal oxide.

Here, in the all solid state battery utilizing thedeposition-dissolution reactions of a metal lithium as an anodereaction, the metal included in the protective layer also expands andcontracts due to intercalation and desorption of Li. For this reason,the protective layer as in Patent Literature 1 has a risk of generationof a crack. When a crack is generated in the protective layer, there isa risk that short circuit may proceed from the crack. In contrast, theprotective layer in the present disclosure contains a polymer, and thusthe crack of the protective layer can be inhibited. As a result, theshort circuit of the all solid state battery can be inhibited. Also, theprotective layer in the present disclosure is capable of suppressing theinterface resistance between the anode active material layer and thesolid electrolyte layer similarly to Patent Literature 1.

1. Protective Layer

The protective layer in the present disclosure is a layer arrangedbetween the later described anode current collector and solidelectrolyte layer, and contains a Mg-containing particle containing atleast Mg, and also contains a polymer.

The Mg-containing particle contains at least Mg. The Mg-containingparticle may be a particle of a simple substance of Mg, and may be aparticle containing Mg and an element other than Mg. Examples of theelement other than Mg may include Li and a metal (including half metal)other than Li. Also, an additional example of the element other than Mgmay be non-metal such as O.

The Mg-containing particle may be an alloy particle containing Mg and ametal other than Mg. In some embodiments, the alloy particle is an alloycontaining Mg as a main component. Examples of a metal M other than Mgin the alloy particle may include Li, Au, Al and Ni. The alloy particlemay contain just one kind of the metal M, and may contain two kinds ormore of the metal M. Also, the Mg-containing particle may or may notcontain Li. In the former case, the alloy particle may include an alloyof β single phase of Li and Mg.

The Mg-containing particle may be an oxide particle containing Mg and O.Examples of the oxide particle may include an oxide of a simplesubstance of Mg, and a composite metal oxide represented by Mg-M′-O,provided that M′ is at least one of Li, Au, Al and Ni. In someembodiments, the oxide particle contains at least Li as M′. M′ may ormay not contain a metal other than Li. In the former case, M′ may be onekind of metal other than Li, and may be two or more kinds. Meanwhile,the Mg-containing particle may not contain 0.

The Mg-containing particle may be a primary particle, and may be asecondary particle which is aggregation of the primary particles. Also,in some embodiments, the average particle size D₅₀ of the Mg-containingparticle is small. When the average particle size is small, thedispersibility of the Mg-containing particle in the protective layerimproves, and reaction point with Li increases; thus, it is effective toinhibit short circuit. The average particle size (D₅₀) of theMg-containing particle is, for example, 500 nm or more, and may be 800nm or more. Meanwhile, the average particle size (D₅₀) of theMg-containing particle is, for example, 20 μm or less, may be 10 μm orless, and may be 5 μm or less.

The proportion of the Mg-containing particle in the protective layer is,for example, 50 weight % or more, may be 60 weight % or more, and may be80 weight % or more. Meanwhile, the proportion of the Mg-containingparticle is, for example, 99 weight % or less, and may be 90 weight % orless. Also, the Mg-containing particle expands and contracts when Li isintercalated and desorbed. In this point, the Mg-containing particle maybe regarded as an active material. In some embodiments, the protectivelayer contains just the Mg-containing particle as an active material,but may contain an additional active material particle. The proportionof the Mg-containing particle with respect to all the active materialsincluded in the protective layer is, for example, 50 weight % or more,may be 70 weight % or more, and may be 90 weight % or more.

Examples of the polymer (binder) may include a fluorine-based binder anda rubber-based binder. Examples of the fluorine-based binder may includepolyvinylidene fluoride (PVDF) and polytetra fluoroethylene (PTFE).Also, examples of the rubber-based binder may include butadiene rubber(BR), acrylate butadiene rubber (ABR), and styrene butadiene rubber(SBR).

The proportion of the polymer in the protective layer is notparticularly limited, but for example, it is 10 weight % or less, may be5 weight % or less, may be 3 weight % or less, and may be 1 weight % orless. Meanwhile, the proportion of the polymer is, for example, 0.1weight % or more.

The thickness of the protective layer is not particularly limited, andfor example, it is 5 μm or more, and may be 15 μm or more. Meanwhile,the thickness of the protective layer is, for example, 100 μm or less,may be 50 μm or less, and may be 30 μm or less. Examples of the methodfor forming the protective layer may include a method of pasting anddrying a mixture containing the Mg-containing particle, a polymer and adispersion medium.

2. Anode

The anode in the present disclosure includes at least an anode currentcollector. As described above, the anode may or may not include an anodeactive material layer.

In some embodiments, when the anode includes an anode active materiallayer, the anode active material layer contains at least one of a simplesubstance of Li and a Li alloy as an anode active material.Incidentally, in the present disclosure, a simple substance of Li and aLi alloy may be referred to as a Li-based active material in general.When the anode active material layer contains the Li-based activematerial, the Mg-containing particle in the protective layer may or maynot contain Li.

For example, in an all solid state battery produced by using a Li foilor a Li alloy foil as the anode active material, and using a particle ofsimple substance of Mg as the Mg-containing particle, the simplesubstance of Mg is presumed to be alloyed with Li at the time of initialdischarge. Meanwhile, in an all solid state battery produced by notarranging an anode active material layer, but using a particle of simplesubstance of Mg as the Mg-containing particle, and using a cathodeactive material containing Li, the simple substance of Mg is presumed tobe alloyed with Li at the time of initial charge.

The anode active material layer may contain just one of a simplesubstance of Li and a Li alloy as the Li-based active material, and maycontain the both of a simple substance of Li and a Li alloy.

In some embodiments, the Li alloy is an alloy containing a Li element asa main component. Examples of the Li alloy may include Li—Au, Li—Mg,Li—Sn, Li—Al, Li—B, Li—C, Li—Ca, Li—Ga, Li—Ge, Li—As, Li—Se, Li—Ru,Li—Rh, Li—Pd, Li—Ag, Li—Cd, Li—In, Li—Sb, Li—Ir, Li—Pt, Li—Hg, Li—Pb,Li—Bi, Li—Zn, Li—Tl, Li—Te and Li—At. The Li alloy may be just one kind,and may be two kinds or more.

Examples of the shape of the Li-based active material may include a foilshape and a granular shape. Also, the Li-based active material may be adeposited metal lithium. As described above, the protective layercontains a polymer (binder), but the anode active material layer may notcontain a binder.

The thickness of the anode active material layer is not particularlylimited; for example, it is 1 nm or more and 1000 μm or less, and may be1 nm or more and 500 μm or less.

Also, examples of the material for the anode current collector mayinclude Cu, Ni, In, Al and C. Examples of the shape of the anode currentcollector may include a foil shape, a mesh shape, and a porous shape.

3. Cathode

In some embodiments, the cathode in the present disclosure includes acathode active material layer and a cathode current collector. Thecathode active material layer in the present disclosure is a layercontaining at least a cathode active material. Also, the cathode activematerial layer may contain at least one of a solid electrolyte, aconductive material, and a binder, as required.

The cathode active material is not particularly limited if it is anactive material having higher reaction potential than that of the anodeactive material, and cathode active materials that can be used in an allsolid state battery may be used. The cathode active material may or maynot contain a lithium element.

Examples of the cathode active material containing a lithium element mayinclude a metal lithium (Li), a lithium alloy, a lithium oxide and otherlithium compounds.

In some embodiments, the Li alloy is an alloy containing a Li element asa main component. Examples of the Li alloy may include Li—Au, Li—Mg,Li—Sn, Li—Si, Li—Al, Li—Ge, Li—Sb, Li—B, Li—C, Li—Ca, Li—Ga, Li—As,Li—Se, Li—Ru, Li—Rh, Li—Pd, Li—Ag, Li—Cd, Li—Ir, Li—Pt, Li—Hg, Li—Pb,Li—Bi, Li—Zn, Li—Tl, Li—Te, Li—At and Li—In.

Examples of the lithium oxide may include a rock salt bed type activematerial such as LiCoO₂, LiMnO₂, LiNiO₂, LiVO₂, andLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂; a spinel type active material such asLi₄Ti₅O₁₂, LiMn₂O₄, LiMn_(1.5)Al_(0.5)O₄, LiMn_(1.5)Mg_(0.5)O₄,LiMn_(1.5)Co_(0.5)O₄, LiMn_(1.5)Fe_(0.5)O₄ and LiMn_(1.5)Zn_(0.5)O₄; andan olivine type active material such as LiFePO₄, LiMnPO₄, LiNiPO₄ andLiCoPO₄.

Examples of other lithium compounds may include LiCoN, Li₂SiO₃, Li₄SiO₄,lithium sulfide (Li₂S) and lithium polysulfide (Li₂S_(x); 2≤x≤8).

Examples of the cathode active material not including a lithium elementmay include a transition metal oxide such as V₂O₅ and MoO₃; a S-basedactive material such as S and TiS₂; a Si-based active material such asSi and SiO₂; and a lithium storing intermetallic compound such as Mg₂Sn,Mg₂Ge, Mg₂Sb and Cu₃Sb.

Also, a coating layer containing an ion conductive oxide may be formedon the surface of the cathode active material. The coating layerprevents the reaction of the cathode active material and the solidelectrolyte, and thus the all solid state battery may have excellentoutput properties. Examples of the ion conductive oxide may includeLiNbO₃, Li₄Ti₅O₁₂ and Li₃PO₄.

The proportion of the cathode active material in the cathode activematerial layer is, for example, 20 weight % or more, may be 30 weight %or more and may be 40 weight % or more. Meanwhile, the proportion of thecathode active material is, for example, 80 weight % or less, may be 70weight % or less, and may be 60 weight % or less.

Examples of the conductive material may include a carbon material.Specific examples of the carbon material may include acetylene black,Ketjen black, VGCF and graphite. The solid electrolyte is in the samecontents as those described in “4. Solid electrolyte layer”. The binderis in the same contents as those described in “2. Anode active materiallayer”. Also, the thickness of the cathode active material layer is, forexample, 0.1 μm or more and 1000 μm or less.

Also, examples of the material for the cathode current collector mayinclude Al, Ni and C. Examples of the shape of the cathode currentcollector may include a foil shape, a mesh shape, and a porous shape.

4. Solid Electrolyte Layer

The solid electrolyte layer in the present disclosure is a layercontaining at least a solid electrolyte. Also, the solid electrolytelayer may contain a binder as required.

Examples of the solid electrolyte may include an inorganic solidelectrolyte such as a halide solid electrolyte, a sulfide solidelectrolyte, an oxide solid electrolyte, and a nitride solidelectrolyte.

In some embodiments, the sulfide solid electrolyte contains, forexample, a Li element, an X element (X is at least one kind of P, As,Sb, Si, Ge, Sn, B, Al, Ga, and In), and a S element. Also, the sulfidesolid electrolyte may further contain at least one of an O element and ahalogen element. Examples of the shape of the solid electrolyte mayinclude a granular shape.

Examples of the sulfide solid electrolyte may include Li₂S—P₂S₅,Li₂S—P₂S₅—LiI, Li₂S—P₂S₅—GeS₂, Li₂S—P₂S₅—Li₂O, Li₂S—P₂S₅—Li₂O—LiI,Li₂S—P₂S₅—LiI—LiBr, Li₂S—SiS₂, Li₂S—SiS₂—LiI, Li₂S—SiS₂—LiBr,Li₂S—SiS₂—LiCl, Li₂S—SiS₂—B₂S₃—LiI, Li₂S—SiS₂—P₂S₅—LiI, Li₂S—B₂S₃,Li₂S—P₂S₅—ZmSn (provided that m, n is a positive number and Z is one ofGe, Zn and Ga), Li₂S—GeS₂, Li₂S—SiS₂—Li₃PO₄, Li₂S—SiS₂-Li_(x)MO_(y)(provided that x, y is a positive number and M is one of P, Si, Ge, B,Al, Ga and In).

The solid electrolyte may be in a glass shape, and may include a crystalphase. Examples of the shape of the solid electrolyte may include agranular shape. The average particle size (D₅₀) of the solid electrolyteis, for example, 0.01 μm or more. Meanwhile, the average particle size(D₅₀) of the solid electrolyte is, for example, 10 μm or less, and maybe 5 μm or less. Ion conductivity of the solid electrolyte at 25° C. is,for example, 1*10⁻⁴ S/cm or more, and may be 1*10⁻³ S/cm or more.

The binder is in the same contents as those described in “1. Protectivelayer”; thus, the descriptions herein are omitted. Also, the thicknessof the solid electrolyte layer is, for example, 0.1 μm or more and 1000μm or less.

5. Other Constitutions

The all solid state battery in the present disclosure may furtherinclude a restraining jig that applies a restraining pressure along withthe thickness direction of the cathode, the solid electrolyte layer andthe anode. As the restraining jig, known jigs may be used. Therestraining pressure is, for example, 0.1 MPa or more and may be 1 MPaor more. Meanwhile, the restraining pressure is, for example, 50 MPa orless, may be 20 MPa or less, may be 15 MPa or less, and may be 10 MPa orless. The smaller the restraining pressure, the more the increase insize of the restraint jig can be suppressed. Meanwhile, the smaller therestraining pressure, the more easily short circuit occurs; however,arrangement of the protective layer in the present disclosure inhibitsthe occurrence of short circuit.

6. All Solid State Battery

The kind of the all solid state battery in the present disclosure is notparticularly limited, but is typically a lithium ion battery. Also, theall solid state battery in the present disclosure may be a primarybattery and may be a secondary battery. The reason therefor is to berepeatedly charged and discharged and useful as a car-mounted batteryfor example.

The all solid state battery in the present disclosure may be a singlebattery and may be a layered battery. The layered battery may be amonopolar layered battery (layered battery connected in parallel), andmay be a bipolar layered battery (layered battery connected in series).Examples of the shape of the battery may include a coin shape, alaminate shape, a cylindrical shape and a square shape.

Incidentally, the present disclosure is not limited to the embodiments.The embodiments are exemplification, and any other variations areintended to be included in the technical scope of the present disclosureif they have substantially the same constitution as the technical ideadescribed in the claims of the present disclosure and have similaroperation and effect thereto.

EXAMPLES Example 1

<Formation of Protective Layer>

To a container made of PP (polypropylene), heptane, a heptane solutioncontaining 5 weight % or butadiene rubber, and Mg particle (simplesubstance of Mg, average particle size: 10 μm, from EM Japan Co., Ltd.)were added, and agitated for 30 seconds by an ultrasonic dispersiondevice (UH-50 from SMT Corporation). Next, the container was shaken for30 minutes by a shaker (TTM-1 from SIBATA SCIENTIFIC TECHNOLOGY LTD.).Thereby, a mixture for a protective layer was prepared. The mixture waspasted on a substrate (Al foil) by a blade method using an applicator.Then, the pasted mixture was dried for 30 minutes on a hot plate at 100°C. Thereby, a protective layer with the substrate was obtained. Thethickness of the protective layer was 15 μm.

<Production of Anode>

A Li foil that was used as an anode active material was placed on ananode current collector (Cu foil), and pressed at 100 MPa. Thereby, ananode including an anode current collector and an anode active materiallayer was obtained.

<Production of Cathode>

A cathode active material (simple substance of sulfur), a sulfide (P₂S₅)and a binder (VGCF) were weighed so as to be S:P₂S₅:VGCF=52.3:19.2:28.3in the weight ratio. These were mixed for 15 minutes with an agatemortar to obtain a raw material mixture. The raw material mixture wasput into a container (45 mL, made of ZrO₂) of a planetary ball mill,ZrO₂ ball (cp=4 mm, 96 g) was further put thereinto, and the containerwas completely sealed. This container was installed to a planetary ballmachine (P7 from Fritsch), and a cycle of: mechanical milling(revolution speed: 510 rpm) for 1 hour, stop for 15 minutes, mechanicalmilling in reverse revolution (revolution speed: 510 rpm) for 1 hour,stop for 15 minutes, was repeated for total 48 hours. Thereby, a cathodemixture was obtained.

Mesitylene and a mesitylene solution containing 5 weight % of SBR wereput into a container, shaken for 3 minutes by a shaker (TTM-1 fromSIBATA SCIENTIFIC TECHNOLOGY LTD.), and mixed for 30 seconds by anultrasonic dispersion device (UH-50 from SMT Corporation). The cathodemixture was put into the container, mixed for 30 seconds by theultrasonic dispersion device, and shaken for 3 minutes by the shaker.This operation was repeated twice. After that, the product was pasted ona current collector (roughen Al foil) using an applicator with 240 μmpasting gap. After that, the product was dried for 30 minutes on a hotplate at 165° C. Thereby, a cathode including a cathode currentcollector and a cathode active material layer was obtained.

<Production of all Solid State Battery>

A sulfide solid electrolyte (Li₂S—P₂S₅-based solid electrolyte includingLiI—LiBr), a binder (heptane solution containing 5 weight % of ABR), anda dispersion medium (butyl butyrate) were added to a PP container. Thesubstances in the container were mixed for 30 seconds by an ultrasonicdispersion device, shaken for 3 minutes by a shaker, and further mixedfor 30 seconds by an ultrasonic dispersion device. Thereby, a mixturefor a solid electrolyte layer was obtained. The mixture was pasted on asubstrate (Al foil) by a blade method using an applicator. After that,the product was dried for 30 minutes on a hot plate at 150° C. Thereby,a transfer member including the substrate and the solid electrolytelayer was obtained.

The cathode and the transfer member were layered so that the cathodeactive material layer and the solid electrolyte layer contacted witheach other, pressed at 600 MPa, and the substrate (Al foil) was peeledoff to obtain a layered body 1. Next, the anode and the protective layerwith the substrate were layered so that the anode active material layerand the protective layer contacted with each other, pressed at 100 MPa,and the substrate was peeled off to obtain a layered body 2. Next, thelayered body 1 and the layered body 2 were layered so that the solidelectrolyte layer and the protective layer contacted with each other,and pressed at 100 MPa to obtain an electrode body. This electrode bodywas sealed in a laminate film, and restrained at 10 MPa by a restrainingmember. Thereby, an all solid state battery was produced.

Example 2

An all solid state battery was produced in the same manner as in Example1 except that a Mg particle having the average particle size of 800 nmwas used.

Comparative Example 1

A protective layer including Au (thickness: 20 nm) was formed instead ofthe protective layer including the Mg particle and the binder. Inspecific, in the production of the transfer member, Au wasvapor-deposited by spattering on the surface of the solid electrolytelayer which was the opposite side surface from the substrate, andthereby a protective layer was produced. An all solid state battery wasproduced in the same manner as in Example 1 except that this transfermember was used.

Comparative Example 2

An all solid state battery was produced in the same manner as in Example1 except that the protective layer was not formed.

Comparative Example 3

An all solid state battery was produced in the same manner as in Example1 except that a LiMg alloy foil was used as the anode active materiallayer and the protective layer was not formed.

[Evaluation]

<Charge and Discharge Test>

A charge and discharge test was respectively conducted to all solidstate batteries produced in Examples 1, 2 and Comparative Examples 1 to3 in the following manners. First, the battery was respectively constantcurrent-constant voltage (CC-CV) discharged at 10 hour rate (0.1 C)until 1.5 V. After that, the battery was respectively charged at 10 hourrate (0.1 C) until 3.0 V. Since the inclination of the charge curveschanges when short circuit occurs, the short circuit capacity wasdefined until that point, and the short circuit capacity wasrespectively measured.

<Impedance Measurement>

An impedance measurement was respectively conducted to each all solidstate battery before conducting the charge and discharge test, and theresistance of that half circle was calculated by fitting to obtaincharge transfer resistivity. Conditions of the impedance measurementwere 10 mV of voltage magnitude and 100 kHz-1 kHz of frequency.

<Li Ratio Measurement>

The Li ratio (atomic ratio of Li with respect to all metals in the anodelayer and the protective layer) in the all solid state battery whenfully charged (SOC: 100%) was respectively calculated. For thecalculation of the Li ratio, the method described in JP-A No.2020-184513 was used. The results are shown in Table 1.

TABLE 1 Li ratio Average when particle Short battery Charge size circuitwas fully transfer Protective of Mg capacity charged resistivity layer(D₅₀) (mAh) (%) (Ω cm²) Comp. Au — 0.117 90 — Ex. 1 Comp. None — 0 100 —Ex. 2 Comp. None — 0.34 90 — Ex. 3 Example 1 Mg  10 μm 0.38 62.5 17.3Example 2 Mg 800 nm 0.62 75 9.6

As shown in Table 1, it was confirmed that the short circuit capacity ofExamples 1 and 2 was respectively larger than that of ComparativeExamples 1 to 3, and the short circuit was inhibited. The reasontherefor was presumed to be because the protective layer with highflexibility was respectively obtained in Examples 1 and 2 since thepolymer was used in addition to the Mg-containing particle. Further, theaverage particle size of Example 2 was smaller than that of Example 1,and the reaction points with Li were more; thus the short circuitcapacity thereof was presumably further larger. Also, short circuitinstantly occurred in Comparative Example 2. This was presumably becausethe restraining pressure in the experiment this time was 10 MPa, whichwas low and the environment where short circuit easily occurs. Incontrast, in Examples 1 and 2, the protective layer including theMg-containing particle and the polymer was respectively arranged, andthus the occurrence of short circuit was inhibited even though theenvironment was low restraining pressure of 10 MPa. Also, it wassuggested that the Li ratio when the battery was fully charged was 62.5%or more and 75% or less.

REFERENCE SIGNS LIST

-   1 anode active material layer-   2 anode current collector-   3 cathode active material layer-   4 cathode current collector-   5 solid electrolyte layer-   6 protective layer-   10 all solid state battery

What is claimed is:
 1. An all solid state battery comprising an anode including at least an anode current collector, a cathode, and a solid electrolyte layer arranged between the anode and the cathode; wherein a protective layer containing a Mg-containing particle that contains at least Mg, and also containing a polymer, is arranged between the anode current collector and the solid electrolyte layer.
 2. The all solid state battery according to claim 1, wherein an anode active material layer containing an anode active material that is at least one of a simple substance of Li and a Li alloy, is arranged between the anode current collector and the protective layer.
 3. The all solid state battery according to claim 1, wherein the anode current collector and the protective layer directly contact with each other.
 4. The all solid state battery according to claim 1, wherein the Mg-containing particle contains Li.
 5. The all solid state battery according to claim 1, wherein the Mg-containing particle does not contain Li.
 6. The all solid state battery according to claim 1, wherein an average particle size D₅₀ of the Mg-containing particle is 800 nm or more and 10 μm or less.
 7. The all solid state battery according to claim 1, wherein a thickness of the protective layer is 5 μm or more and 100 μm or less.
 8. The all solid state battery according to claim 1, further comprising a restraining jig that applies restraining pressure along with a thickness direction of the cathode, the solid electrolyte layer and the anode; wherein a restraining pressure to be applied by the restraining jig is 20 MPa or less. 